As one of the integrated circuit devices, known in order to realize a high integration density mounting is such construction that single or plurality of integrated circuit elements (chips) are built into a small size ceramic package called the chip carrier, plurality of said chip carriers are mounted on a ceramic wiring board called a mother board, and these are electrically connected by soldering etc.
In such integrated circuit devices having such construction, said chip carrier is usually electrically connected by soldering the electrode material formed at the rear surface or the perimeter of a side of the chip carrier and the electrode material formed on an upper surface of the mother board, without using external connecting terminals.
Said chip carrier and mother board are assembled into an integrated unit by the following process. Namely, the chip carrier and mother board are dipped into the melting solder respectively, then solder pad is formed on the electrode material and solder pads of both chip carrier and mother board are located for positioning and heated for soldering.
FIG. 1 shows a part of cross section of a conventional integrated circuit device where a chip carrier and mother board are built into a single unit by soldering. In this figure, 1 denotes a chip carrier; 2 denotes a mother board; 3 denote soldered electrodes; 4 indicate external connecting terminals led out from the mother board 2.
In this construction where the electrode material is directly soldered, a gap between the rear side (lower side) of the chip carrier and the upper side (surface) of the mother board is very narrow, and when the flux used in the soldering is remained or dust exists in such gap, it is difficult to remove such contamination or dust by the cleaning using ordinary organic solvent.
Because the organic solvent does not circulate sufficiently into such a narrow gap in such a cleaning method that contamination or dust is solved and removed when an integrated device is dipped into the circulating solution of an organic solvent of the trichloroethylene or Freon etc. which is a fusible agent of flux or into the gaseous ambient of the organic solvent. In addition, when mounting a mother board loading a chip carrier on to a printed wiring board comprising a polymer resin, the external connecting terminals of mother board are dipped into the fused solder for the purpose of solder coating. Such solder coating brings about a problem that flux and fused solder migrate into said narrow gap between the mother board and chip carrier through a space between the external connecting terminals and said printed wiring board.
Thereby the relevant integrated circuit devices have resulted in short circuit between electrodes and increase of leak current.